25. 7. 2013. Seminar: Jaćim Jaćimović

Thursday 25 July 2013 at 12PM
IPB Library

др Јаћим Јаћимовић
Laboratory of Physics of Complex Matter, EPFL, Switzerland

Nature of charge carriers and mechanism of conductivity in anatase TiO2

Abstract:

Titanium dioxide (TiO2) a wide band gap semiconductor emerged as one of the most promising functional materials. In nature it occurs in there different forms: rutile, brookite and anatase. The anatase phase attracts the largest attention since it is essential for fabrication of dye sensitized solar cells, memristors and of photocatalitic devices. Recently, anatase has been discovered to be an ideal host for magnetic ions, arising as a candidate to marry semiconductor technology and the advantages of spintronics information development. Oxygen vacancies are known to be the native defects in the crystal structure giving rise to the existence of the shallow donor level. We present here results of a detailed study of oxygen deficient single crystal samples obtained by means of transport coefficient, THz optical conductivity, ARPES and STM measurements. Strong evidences for the existence of large polarons with diameter much smaller than typical size of anatase nanoparticles and nanowires are found. We show that mass of the polarons and their mobility depends of the polaron concentration. It was observed that electron phonon interaction rules the conductivity in anatase phase. Ultimately, we discovered that polaronic nature of the charge carriers results in one more distinctive feature of this compound, it is huge Seebeck coefficient which puts this material as a potential thermoelectric.

[1] J. Jaćimović, C. Vâju, R. Gaál, A. Magrez, H. Berger, L. Forró , V. Cerovski and R. Zikić “Pressuredependence of the large polaron transport in anatase TiO2 singlecrystals” European Physics Letter, 99, (2012),57005.

[2] J. Jaćimović, R. Gaál, A. Magrez, L. Forró, M. Regmi, G. Eres, Electrical property measurements ofCr-N codoped TiO2 epitaxial thin films grown by pulsed laserdeposition, Appl. Phys. Lett. 102, 172108 (2013).

[3] J. Jaćimović, R. Gaál, A. Magrez, J. Piatek, L. Forró, S. Nakao, Y. Hirose, and T. Hasegawa, Lowtemperature resistivity, thermoelectricity, and power factor of Nb dopedanatase TiO2, Appl. Phys. Lett. 102, 013901 (2013)

[4] S. Moser*, L. Moreschini*, J. Jaćimović *, O. S. Barısic, H. Berger, A. Magrez, A. Bostwick, E. Rotenberg, L. Forro and M. Grioni, Tunable polaronic conduction inanatase TiO2, Phys. Rev. Lett. 110, 196403 (2013)